Evolution of the
Butterfly Valve Seal

Resilient Seal

Original
butterfly valve had shaft penetration through the seal
plane. Dowel pin through disc and shaft often
leaked. Note the interference between the seal and
the disc which is needed to effect a tight seal. This
will wear with use and eventually leak.

High
Performance Seal

The next step in butterfly valve
evolution was to move the shaft from the seal plane.
Dowel pin parallel to disc does not leak. Note that
this design also relies upon interference for sealing
and will also eventually leak.

TRICENTRIC® Metal Seal

The triple eccentricity with the
metal seal is the final step in the evolution. Square
keys are utilized for torque transmission. Since
there is no interference between mating parts during
closure, seal wear is eliminated and the seal actually
becomes tighter with use. Tight shut-off up to
1200°F.